Method of nucleating aluminum

ABSTRACT

Silver precipitating nuclei are deposited on a grained aluminum support such that said support can be used as a photolithographic receiving surface in a silver salt diffusion process by contacting the support with an alkaline bath and then contacting with an aqueous silver salt solution. In an alternative one-step treatment, an alkaline solution containing the silver salt is used.

United States Patent [72] Inventor Edward C. Yackel Pittsiord, NT.

[21] Appl. No. 761,852

[22] Filed Sept. 23, 1968 [45] Patented Dec. 21, 1971 {73] AssigneeEastman Kodak Company Rochester, NY.

[54] METHOD OF NUCLEATING ALUMINUM 7 Claims, No Drawings [52] U.S.Cl117/34, 117/50, 117/130 R, 96/29, 96/33 [51] Int. Cl B44d1/092, 844d1/02 [50] Field of Search 117/50, 34, 130 R; 96/29, 33

{56] Reierenees Cited UNITED STATES PATENTS 2,390,944 12/1945 King117/50 X 3,186,842 6/1965 De Haes et al.... 96/33 X 3,278,958 10/1966Regan et al. 96/33 X 3,300,306 l/1967 Sevens et al. 96/33 X FOREIGNPATENTS 934,693 8/1963 Great Britain 96/29 Primary Examiner-Alfred L.Leavitt Assistant Examiner- Edward G. Whitby Att0rneysW. H. J. Kline, B.D. Wiese and H. E. Byers METHOD OF NUCLEATING ALUMINUM This inventionrelates to a method of preparing lithographic printing forms,particularly to lithographic printing plates made photographically.

The invention is concerned with the production of metallic plates foruse in making lithographic printing plates by the silver salt diffusionprocess. As explained in British Pat. specification, Ser. No. 934,691,the silver salt diffusion process is a widely used commercial processwherein an imagewise exposed silver halide emulsion layer is developedin the presence of a silver halide solvent in such a manner that theundeveloped silver halide diffuses into the adjacent receiving sheet,where it is developed to give the desired image. The development nucleisuch as silver nuclei deposited on the receiving sheet receive thedeveloped silver from the difi'using silver halide and thus an image isformed thereon.

When using such a receiving sheet or support in lithography, both waterand a greasy ink are applied and the support is sufficiently hydrophilicto accept water preferentially to the greasy ink, while the oleophilicimage accepts ink preferentially to the water. Hence, to obtain goodprints it is necessary that the difference in hydrophilic and oleophilicproperties of the image and the background surface of the receivingsheet be sufficiently great that when water and ink are applied, theimage will accept sufficient ink without the background accepting anyink at all.

The practice in making a photolithographic printing plate is to producean oleophilic image on hydrophilic support which can be put into aninking machine whereby large numbers, up to 20,000 copies can usually bemade very rapidly from the one plate.

in known processes wherein a silver image is formed on a receiving sheetby the silver salt diffusion process described above, it is usual toapply to the receiving surface on which the desired silver image isformed a gelatin solution containing both the development nuclei such assilver and a colloidal binder in which the nuclei are embedded. However,it is not possible to use the image developed therein as a lithographicprinting plate because on wetting the layer for the purpose of makingthe nonsilver areas oleophobic, the gelatin of the silver areas is alsorendered oleophobic. Thus, the silver image formed on the support doesnot accept sufficient ink to serve as a useful lithographic printingplate.

To remedy this very serious problem, extensive research has been and ispresently underway to discover commercially practicable methods wherebydevelopment nuclei can be deposited on a satisfactory receiving surfacewithout the use of a gelatin binder. As described in the aforementionedBritish Pat. specification, it has been found that a suitably grainedand/or anodized aluminum sheet provides an excellent hydrophilicreceiving surface for the development nuclei.

Various experimental tests have been conducted on such an aluminumsupport on which silver nuclei have been deposited. Although it has beenestablished that aluminum receiving sheets containing silver nucleideposited thereon are very satisfactory and are especially useful in theproduction of silver salt sensitized lithographic printing plates, ithas also been recognized that the deposition of the nuclei on thereceiving sheet (or nucleation of the receiving sheets as it is oftenreferred to in the art) is a rather involved and somewhat uncertainprocess in which the interdependence of the various operations such asgraining, anodizing, and application of the nuclei are not wellunderstood and frequently result in an unsatisfactory material.

In other known processes such as that described in British Pat.specification, Ser. No. 934,692, nucleation of anodized and/or grainedmetallic surfaces requires treatment of the metallic surface with anaqueous colloidal dispersion of silver or gold particles. Althoughsatisfactory results have been ob tained by this process, the process islimited to aqueous colloidal dispersions of the element to be depositedon the receiving surface. Thus, use of the water-soluble silver saltssuch as silver nitrate and silver acetate, etc. which are the silversalts generally utilized and preferred in commercial lithographicprocesses is prohibited.

According to one aspect of the present invention there is provided amethod of depositing development nuclei on a grained aluminum supportwhich comprises the steps of treating said grained aluminum support withan alkaline bath and subjecting said aluminum support to furthertreatment with an aqueous silver salt solution, thereby providing anucleated aluminum support adaptable for use as a lithographic receivingsheet. in accordance with a preferred embodiment of the presentinvention the above recited steps of treating the grained aluminumsupport with an alkaline bath and then subjecting said grained aluminumsupport to further treatment with an aqueous silver salt solution canadvantageously be performed simultaneously by initially dissolving thesilver salt in the alkaline bath, thus yielding a single step process.

Several important aspects of the present invention should beparticularly noted. First, it can be seen that the present inventionrequires only that the aluminum support be grained. Anodizing thesupport is unnecessary. Secondly, no colloidal binder is used. Treatmentof the aluminum support with a colloidal dispersion of the element to bedeposited thereon is eliminated; thus the commercially preferredwater-soluble silver salts can be used. And fourth, the entire process,either the two step or the one step embodiment, can be accomplished inno more than 60 seconds. Thus, not only is the process of the presentinvention simple and reliable, but the extreme rapidity of the entireprocess represents a clear advance over known prior art techniques.

It has been found that the soluble silver salt contained dis solved inthe aqueous bath used according to the present invention can be aninorganic, water-soluble salt such as silver nitrate, silver nitrite,silver sulfate, silver perchlorate, and the like, or it can be anorganic silver salt such as silver acetate or silver lactate. Althoughthe silver lactate, silver nitrate or silver acetate salts arepreferred, it is believed that almost any water-soluble silver saltwould give useful results. Other cations can also be used instead ofsilver or in addition to silver, provided they are more electropositivethan aluminum.

The foregoing silver salts are especially useful in the above describedtwo step embodiment of the present invention wherein a grained aluminumsupport is first bathed in an alkaline solution followed by furthervbathing in the aqueous silver salt solution. In this embodiment the stepof bathing in an alkaline medium is readily accomplished through the useof a large number of suitable basic solutions. Aqueous solutions of thealkali and alkaline-earth metal hydroxides, oxides and anhydrides areuseful. The only real limitation is of course that the particular basicmaterial selected must be water-soluble. lt has been found that 0.1normal solutions of potassium, ammonium and sodium hydroxide serve aspreferred alkaline baths. The concentration of the alkaline solutionwill vary depending on the desired pH. However, neither theconcentration of basic material nor the particular degree of alkalinityis considered to be a critical factor. For instance, as noted above,preferred alkaline baths include an aqueous solution of a strong basesuch as sodium hydroxide as well as a weak base such as ammoniumhydroxide. Alkaline solutions having a pH within the range of about 10to 14 are acceptable for use according to the instant invention,including both the two step embodiment and the one-step embodimentdiscussed immediately hereinafter.

With respect to the above-described one-step embodiment of the presentinvention wherein the step of bathing the grained aluminum support in analkaline bath is performed simultaneously with the further step ofsubjecting the aluminum support to bathing in an aqueous bath of solublesilver salt, it has been found preferable to use a bath containing asilver salt dissolved in ammonium hydroxide to which an aqueous solutionof sodium hydroxide has been subsequently added. Such a bath, whereinthe silver salt, for example silver nitrate, is initially incorporatedin the alkaline bath, upon contact with a grained aluminum support,results in a simple single step process for the production of nucleatedaluminum receiving sheets.

The method of the present invention for deposition of the developmentnuclei wherein the grained aluminum surface is treated by bathing in anaqueous solution of the silver salt ensures that the amount of thesilver nuclei deposited on the surface per unit area is low. Silver saltsolutions which may be used in either the above described one-step ortwo-step embodiments contain between about 0.2 and 0.0005 mole of silversalt per litre.

The grained aluminum support (or foil as it is referred to in the art)utilized in the present invention can be prepared by any of a variety ofwell-known techniques. A suitably grained sheet bearing a fine sharplithographic grain has been produced by a chemical etching technique, asuitable material for conventional platemaking being that soldcommercially by Addressograph Multigraph. Other suitable techniquesinclude mechanical brushing or grinding. In any event, a wide variety ofdiverse techniques are known and can be utilized. The fact that the foilis grained ensures that the foil is sufficiently hydrophilic and alsoensures the absence of contaminants such as oil.

The following examples are included for a further understanding of theinvention:

EXAMPLE 1 A brushed-grained aluminum support 0.005 inch thick is placedin an 0.5 percent aqueous bath of sodium hydroxide for 30 seconds atroom temperature and the excess removed by water rinse.

Immediately, thereafter, the brushed grained aluminum support is placedin a 0.l N aqueous silver acetate bath for 30 seconds at roomtemperature, rinsed and dried.

The aforesaid nucleated aluminum support is then coated with anemulsion, contact exposed to a line positive, developed and furthertreated as described in British Pat. specification, Ser. No. 934,691,after which its press performance is that of a satisfactory lithographicprinting plate.

EXAMPLE 2 In this example, a nucleated aluminum foil is preparedaccording to the process of example 1 except a solution of 0.] N aqueoussilver lactate is substituted for the aqueous silver acetate bath.

EXAMPLE 3 In this example, a nucleated aluminum foil is preparedaccording to the process of example 1 except a solution of 0.1 N aqueoussilver nitrate is substituted for the aqueous silver acetate bath.

EXAMPLE 4 In this example, a nucleated aluminum foil is preparedaccording to the process of example 1 except a solution of 0.5 percentaqueous potassium hydroxide is substituted for the sodium hydroxidebath.

EXAMPLE 5 In this example, concentrated ammonium hydroxide is added to0.l N silver nitrate in sufficient excess quantity to form silverhydroxide and dissolve it. To this solution is added a 0.1 N solution ofsodium hydroxide equivalent to the silver. The resultant aqueousalkaline solution already containing the silver salt completelydissolved therein is then used as a bathing solution. That is, a grainedaluminum foil identical to that described in example 1 is bathed in thealkaline solution for one minute at room temperature, rinsed and dried.

The resultant grained aluminum support having silver nuclei depositedthereon is then further treated as described in example 1 above, theresult of which is the production of a satisfac tor lithographic rintingplate.

he invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinaloove and as set forth in the appendedclaims.

lclaim:

l. A method of depositing development nuclei on a grained aluminumsupport which comprises the steps of treating said grained aluminumsupport with an aqueous bath selected from the class consisting of thealkali and alkaline earth metal hydroxides and oxides and ammoniumhydroxide baths and subjecting said aluminum support to furthertreatment with an aqueous silver salt solution, thereby providing anucleated aluminum support adaptable for use as a lithographic receivingsheet.

2. A method of depositing development nuclei on a grained aluminumsupport according to claim ll wherein the steps of treating the grainedaluminum support with an aqueous bath selected from the class consistingof the alkali and alkaline earth metal hydroxides and oxides andammonium hydroxide baths and then subjecting said grained aluminumsupport to treatment with an aqueous silver salt solution are performedsimultaneously by initially dissolving the silver salt in said baththereby yielding a single step process.

3. A method for depositing development nuclei on a grained aluminumsupport according to claim 2 wherein the said bath consists of aalkaline silver nitrate solution containing ammonium hydroxide andsodium hydroxide.

4. A method of depositing development nuclei on a grained aluminumsupport according to the method of claim 1 wherein said bath is a memberselected from the group consisting of an aqueous solution of potassiumhydroxide, an aqueous solution of ammonium hydroxide, and an aqueoussolution of sodium hydroxide.

5. A method of depositing development nuclei on a grained aluminumsupport according to the method of claim 1 wherein the silver saltdissolved in said aqueous silver salt solution is a member selected fromthe group consisting of silver nitrate, silver acetate, and silverlactate.

6. A method of depositing development nuclei on a grained aluminumsupport according to the method of claim I wherein the said bath is amember selected from the group consisting of an aqueous solution ofsodium hydroxide, an aqueous solution of potassium hydroxide, and anaqueous solution of ammonium hydroxide; and wherein the silver saltdissolved in said aqueous silver salt solution is a member selected fromthe group consisting of silver acetate, silver nitrate, and silverlactate.

7. A method of depositing development nuclei on a grained aluminumsupport according to the method of claim ti) wherein said silver salt issilver nitrate.

2. A method of depositing development nuclei on a grained aluminumsupport according to claim 1 wherein the steps of treating the grainedaluminum support with an aqueous bath selected from the class consistingof the alkali and alkaline earth metal hydroxides and oxides andammonium hydroxide baths and then subjecting said grained aluminumsupport to treatment with an aqueous silver salt solution are performedsimultaneously by initially dissolving the silver salt in said baththereby yielding a single step process.
 3. A method for depositingdevelopment nuclei on a grained aluminum support according to claim 2wherein the said bath consists of a alkaline silver nitrate solutioncontaining ammonium hydroxide and sodium hydroxide.
 4. A method ofdepositing development nuclei on a grained aluminum support according tothe method of claim 1 wherein said bath is a member selected from thegroup consisting of an aqueous solution of potassium hydroxide, anaqueous solution of ammonium hydroxide, and an aqueous solution ofsodium hydroxide.
 5. A method of depositing development nuclei on agrained aluminum support according to the method of claim 1 wherein thesilver salt dissolved in said aqueous silver salt solution is a memberselected from the group consisting of silver nitrate, silver acetate,and silver lactate.
 6. A method of depositing development nuclei on agrained aluminum support according to the method of claim 1 wherein thesaid bath is a member selected from the group consisting of an aqueoussolution of sodium hydroxide, an aqueous solution of potassiumhydroxide, and an aqueous solution of ammonium hydroxide; and whereinthe silver salt dissolved in said aqueous silver salt solution is amember selected from the group consisting of silver acetate, silvernitrate, and silver lactate.
 7. A method of depositing developmentnuclei on a grained aluminum support according to the method of claim 6wherein said silver salt is silver nitrate.